The present invention is directed to a method for manufacturing colored striped paper or security paper, and more particularly, to a method for manufacturing colored striped paper by introducing one or more coloring agents to the pulp before the pulp enters the headbox.
Paper is typically manufactured by forming a pulp slurry, which is a mixture of fibers suspended in a solution of primarily water. The fibers can be, for example, cellulose-based fibers (i.e. wood fibers), in which case the slurry is termed pulp slurry. Once the pulp or slurry is produced, it is fed to a distribution system that includes a dilution water header, a distributor, and a headbox. The distributor receives the incoming pulp slurry and is typically utilized to normalize the properties of the slurry, such as its consistency, pressure, and velocity. The dilution water header supplies dilution water that is used to control the consistency of the pulp exiting the distributor. Flow exiting the distributor is fed through a plurality of delivery lines that deliver the flow to a series of nozzles distributed across the headbox. The nozzles deposit the slurry, in xe2x80x9cjetxe2x80x9d form, onto a moving papermaking xe2x80x9cwirexe2x80x9d to form a sheet on the papermaking wire. The sheet is then dewatered, pressed, dried, and treated to form the finished product.
It may be desired to make colored paper that has stripes that extend in the machine direction (i.e. extend in the longitudinal direction of the deposited sheet). However, in order to make colored paper in conventional papermaking systems, dyes, pigments or other colorants are added to the pulp slurry such that all of the pulp slurry is dyed, and the resultant paper web is uniformly colored throughout its thickness. This method does not allow for the selective introduction of color, and therefore the color of the finished paper product is limited to a single shade or color. Some paper mills produce paper sheets having a colored xe2x80x9cmarbledxe2x80x9d appearance. These sheets are manufactured by drizzling small droplets of dye from a pipe located a few inches above the freshly deposited pulp on the wire. This method of dye application produces a random marbled appearance and does not produce a striped paper. In addition, the marbled coloring is located predominately on the top side of the sheet, and is not uniformly distributed throughout the thickness of the paper. Furthermore, when the paper is cut or torn, the uncolored sublayers of the paper become visible. Accordingly, there is a need for a method of manufacturing machine direction striped paper that is colored throughout the entire thickness of the sheet.
The present invention is a method for manufacturing colored striped paper, wherein the colored portions of the paper are colored throughout the thickness of the paper. Paper produced with the inventive method may be used to manufacture printing and writing paper, text, cover, and other specialty grades of paper. The method of the present invention may also be used to produce security paper that is used in the production of documents to help verify the documents"" validity, such as checks, tickets, legal documents, personal identifications, and the like. The present invention adds color to the slurry before the slurry is introduced to the headbox in such a way that the colored and uncolored fibers form a sheet of paper having a machine direction striped pattern throughout the entire thickness of the sheet. The method of the present invention can be practiced by modifying some specific types of existing paper manufacturing equipment, and thus is quick and relatively inexpensive to implement.
Besides adding colorants, the method may also be used to introduce nearly any additive that varies the characteristics of the paper in the cross machine direction. For example, security additives may be added to the paper to help identify documents for security purposes.
In particular, the present invention is a method for manufacturing paper having colored stripes, the method comprising the steps of feeding a slurry to a distributor and delivering the slurry from the distributor to a headbox through a plurality of delivery lines. The delivery lines are coupled to the headbox at a plurality of locations spaced across the headbox in a crossmachine direction. The method further comprises the steps of selectively introducing a first coloring agent in at least two of the delivery lines to selectively color the slurry passing through the at least two delivery lines and depositing the slurry received by the headbox on a papermaking wire to form striped paper.
Other objects and advantages of the present invention will be apparent from the following description and the accompanying drawings.